A mechanism for stroma formation (development of vasculature and supportive connective tissue) is suggested in an experimental "pushing-type" colorectal carcinoma liver metastasis model. The key element is the appearance of smooth muscle actin (SMA)-positive cells and the sinusoidal lakes at the border of the metastases. These lakes are the consequence of the disappearance ('stepping back' of hepatocytes from the border zone, resulting in the fusion of partially capillarized sinusoids. The growing tumor incorporates SMA-expressing cells and sinusoidal lakes. SMA-positive cells produce collagenous matrix, whereas the lakes become the central vessels within the connective tissue columns. Formation of these columns within the tumor is a consequence of the compression atrophy of the base of the incorporated liver tissue, leading to partial separation of the innermost part of the invagination containing functional vessel(s) from the surrounding liver.
Copyright 2005 Wiley-Liss, Inc.